A monomer recovery method and system in a polystyrene production process

Abstract

The present application relates to a kind of monomer recovery method and its system in polystyrene production process;Provide a kind of monomer recovery system in polystyrene production process, comprising: before devolatilization cold, after devolatilization cold, recovery column reboiler, recovery column condenser, before devolatilization cold tank, after devolatilization cold tank, recovery column backflow tank, recovery column cut water tank, front condensate pump, after condensate pump, column kettle pump, reflux pump, heat conduction oil circulating pump and recovery column;In the present application, the vapor phase that devolatilizer is removed, is condensed in two stages;Most oligomers are condensed into liquid phase in before devolatilization cold and are sent into recovery column refining;The condensate of after devolatilization cold is directly recycled back, reduces the load of recovery column system, saves equipment investment and energy consumption;Recovery column reboiler heating uses the warm oil generated by polymerization reactor heat removal as heat source, without additional heating, saves utility consumption.

Description

Technical Field

[0001] This invention relates to a monomer recovery and purification method, and more particularly to a monomer recovery method and system in the polystyrene production process. Background Technology

[0002] In the polystyrene production process, the polymerization reaction conversion rate is about 80%. The remaining unpolymerized monomers and solvents are removed by an devolatilizer and recycled. The unreacted monomers removed by the devolatilizer contain oligomers. If they are directly recycled back to the polymerization reaction, the oligomers will accumulate in the system and affect the quality of the final product.

[0003] Therefore, there is an urgent need for a monomer recovery and refining method that can both remove oligomers from the recovered monomers and ensure product quality, while also reducing equipment investment and saving energy. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a method and system for monomer recovery in the polystyrene production process.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] The first aspect of the present invention is to provide a monomer recovery system in the polystyrene production process, comprising: a pre-cooler for devolatilization, a post-cooler for devolatilization, a reboiler for the recovery tower, a condenser for the recovery tower, a pre-cooling tank for devolatilization, a post-cooling tank for devolatilization, a reflux tank for the recovery tower, a water-cutting tank for the recovery tower, a pre-condensate pump, a post-condensate pump, a bottom pump, a reflux pump, a heat transfer oil circulation pump, and a recovery tower.

[0007] The devolatilizer's outlet is connected to the inlet of the pre-cooler, the pre-cooler's outlet is connected to the inlet of the post-cooler, and the pre-cooler's outlet is connected to the first inlet of the recovery tower. The post-cooler's outlet is connected to the inlet of the vacuum system, and the post-cooler's outlet is connected to the inlet of the polymerization reactor. The recovery tower's outlet is connected to the first inlet of the reboiler, and the reboiler's outlet is connected to the inlet of the recovery tower. The recovery tower's outlet is connected to the inlet of the condenser, and the condenser's outlet is connected to the vacuum system. The condenser's outlet is connected to the inlet of the reflux tank. The reflux tank's first outlet is connected to the second inlet of the recovery tower, and the reflux tank's second outlet is connected to the drainage section.

[0008] All connections are pipe connections.

[0009] Preferably, the reboiler of the recovery tower is heated by a heat transfer oil circulation pipeline. The first and second outlets of the hot oil section are respectively connected to the inlet pipeline of the heat transfer oil circulation pump. The outlet of the heat transfer oil circulation pump is connected to the second inlet pipeline of the recovery tower reboiler. The outlet of the recovery tower reboiler is connected to both the inlet pipeline of the hot oil section and the inlet pipeline of the heat transfer oil circulation pump. A temperature sensor is also connected via a pipeline between the outlet of the heat transfer oil circulation pump and the second inlet of the recovery tower reboiler. Control valves are connected via pipelines between the first and second outlets of the hot oil section and the inlet of the heat transfer oil circulation pump. The temperature sensor is electrically connected to the control valve.

[0010] Preferably, the outlet of the devolatilization cooler and the inlet of the polymerization reactor are sequentially connected by a pipeline to the devolatilization cooler tank and the post-condensate pump; one end of the first pressure balancing pipeline is connected to the outlet pipeline of the devolatilization cooler tank, and the other end of the first pressure balancing pipeline is connected to the inlet pipeline of the vacuum system.

[0011] Preferably, the precooling tank and the precondensate pump are sequentially connected by a pipeline between the outlet of the precooling tank and the first inlet of the recovery tower; one end of the second pressure balancing pipeline is connected to the outlet pipeline of the precooling tank, and the other end of the second pressure balancing pipeline is connected to the inlet pipeline of the postcooling tank.

[0012] Preferably, the bottom pump is connected by a pipeline between the outlet of the recovery tower and the first inlet of the reboiler of the recovery tower; a waste monomer recovery branch is provided between the bottom pump and the first inlet of the reboiler of the recovery tower, and the outlet of the waste monomer recovery branch is connected to the pipeline of the waste monomer treatment section.

[0013] Preferably, the reflux pump is connected by a pipeline between the first liquid outlet of the recovery tower reflux tank and the second liquid inlet of the recovery tower.

[0014] More preferably, a monomer recovery branch is provided between the reflux pump and the second inlet of the recovery tower, and the outlet of the monomer recovery branch is connected to the inlet of the polymerization reactor.

[0015] Preferably, one end of the third pressure balancing pipe is connected to the outlet pipe of the recovery tower reflux tank, and the other end of the third pressure balancing pipe is connected to the inlet pipe of the recovery tower condenser.

[0016] Preferably, the second outlet of the recovery tower reflux tank is connected to the drainage section via a pipeline of the recovery tower water cutter tank, and the outlet of the recovery tower water cutter tank is connected to the inlet pipeline of the vacuum system.

[0017] A second aspect of the present invention is to provide a monomer recovery method in the polystyrene production process, employing the aforementioned monomer recovery system, comprising the following steps: inputting the devolatilized gas phase from the devolatilizer into the devolatilization precooler for primary condensation; the gas phase after primary condensation into the devolatilization postcooler for secondary condensation; the liquid phase after primary condensation into the recovery tower for distillation; the gas phase after secondary condensation into the vacuum system; the liquid phase after secondary condensation returned to the polymerization reactor; the gas phase after distillation into the vacuum system; the first liquid phase after distillation returned to the recovery tower; the second liquid phase returned to the polymerization reactor; and the third liquid phase entering the discharge section.

[0018] The present invention adopts the above technical solution and has the following technical effects compared with the prior art:

[0019] In this invention, the vapor phase removed by the devolatilizer is condensed in two stages; most of the oligomers are condensed into liquid phase in the pre-devolatilizer cooler and sent to the recovery tower for refining; the condensate from the post-devolatilizer cooler is directly recycled back, reducing the load on the recovery tower system and saving equipment investment and energy consumption; the reboiler heating of the recovery tower uses the warm oil generated by the deheating of the polymerization reactor as the heat source, eliminating the need for additional heating and saving on utility costs. Attached Figure Description

[0020] Figure 1 This is a flowchart of the monomer recovery system in the polystyrene production process of the present invention;

[0021] The reference numerals in the figure include:

[0022] Deviation unit 1; Vacuum system 2; Polymerization reactor 3; Hot oil section 4; Drainage section 5; Waste monomer treatment section 6; Deviation precooler E01; Deviation postcooler E02; Reboiler of recovery tower E04; Condenser of recovery tower E05; Precooler of deviation D01; Postcooler of deviation D02; Reflux tank of recovery tower D05; Water cut-off tank of recovery tower D06; Front condensate pump P01; Back condensate pump P02; Boiler pump P04; Reflux pump P05; Heat transfer oil circulation pump P06; Recovery tower C01; Temperature sensor TC. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0025] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of the invention.

[0026] Example 1

[0027] This embodiment provides a monomer recovery system in the polystyrene production process, including: a pre-cooler E01, a post-cooler E02, a reboiler E04, a condenser E05, a pre-cooler D01, a post-cooler D02, a reflux tank D05, a water cut-off tank D06, a pre-condensate pump P01, a post-condensate pump P02, a bottom pump P04, a reflux pump P05, a heat transfer oil circulation pump P06, and a recovery tower CO1;

[0028] The outlet of the devolatilizer 1 is connected to the inlet pipe of the devolatilizer precooler E01, the outlet of the devolatilizer precooler E01 is connected to the inlet pipe of the devolatilizer postcooler E02, the liquid outlet of the devolatilizer precooler E01 is connected to the first liquid inlet pipe of the recovery tower C01, and the devolatilizer precooler tank D01 and the pre-condensate pump P01 are sequentially connected between the liquid outlet of the devolatilizer precooler E01 and the first liquid inlet of the recovery tower C01; one end of the second pressure balancing pipe is connected to the outlet pipe of the devolatilizer precooler tank D01, and the other end of the second pressure balancing pipe is connected to the inlet pipe of the devolatilizer postcooler E02.

[0029] The outlet of the devolatilization aftercooler E02 is connected to the inlet pipe of the vacuum system 2, and the outlet of the devolatilization aftercooler E02 is connected to the inlet pipe of the polymerization reactor 3. The devolatilization aftercooler D02 and the post-condensate pump P02 are connected in sequence between the outlet of the devolatilization aftercooler E02 and the inlet of the polymerization reactor 3. One end of the first pressure balancing pipe is connected to the outlet pipe of the devolatilization aftercooler D02, and the other end of the first pressure balancing pipe is connected to the inlet pipe of the vacuum system 2.

[0030] The outlet of the recovery tower C01 is connected to the first inlet of the recovery tower reboiler E04 via a pipeline, and the bottom pump P04 is connected between the outlet of the recovery tower C01 and the first inlet of the recovery tower reboiler E04 via a pipeline.

[0031] A waste monomer recovery branch is provided between the bottom pump P04 and the first inlet of the reboiler E04 of the recovery tower. The outlet of the waste monomer recovery branch is connected to the pipeline of the waste monomer treatment section 6. The outlet of the reboiler E04 of the recovery tower is connected to the inlet pipeline of the recovery tower CO1. The outlet of the recovery tower CO1 is connected to the inlet pipeline of the condenser E05 of the recovery tower. The outlet of the condenser E05 of the recovery tower is connected to the pipeline of the vacuum system 2. The outlet of the condenser E05 of the recovery tower is connected to the inlet pipeline of the reflux tank D05 of the recovery tower. The first outlet of the reflux tank D05 of the recovery tower is connected to the second inlet pipeline of the recovery tower CO1. The first outlet of the reflux tank D05 of the recovery tower is connected to the pipeline of the recovery tower CO1. The second inlet of 01 is connected to the reflux pump P05 via a pipeline. A monomer recovery branch is provided between the reflux pump P05 and the second inlet of the recovery tower C01. The outlet of the monomer recovery branch is connected to the inlet of the polymerization reactor 3. One end of the third pressure balancing pipeline is connected to the outlet pipeline of the recovery tower reflux tank D05, and the other end of the third pressure balancing pipeline is connected to the inlet pipeline of the recovery tower condenser E05. The second outlet of the recovery tower reflux tank D05 is connected to the drainage section 5 via a pipeline. The second outlet of the recovery tower reflux tank D05 and the drainage section 5 are connected to the recovery tower water cutter tank D06 via a pipeline. The outlet of the recovery tower water cutter tank D06 is connected to the inlet pipeline of the vacuum system 2.

[0032] The reboiler E04 of the recovery tower is heated by a heat transfer oil circulation pipeline. The first and second outlets of the hot oil section 4 are respectively connected to the inlet pipeline of the heat transfer oil circulation pump P06. The outlet of the heat transfer oil circulation pump P06 is connected to the second inlet pipeline of the reboiler E04 of the recovery tower. The outlet of the reboiler E04 of the recovery tower is connected to the inlet pipeline of the hot oil section 4 and the inlet pipeline of the heat transfer oil circulation pump P06. A temperature sensor TC is also connected by a pipeline between the outlet of the heat transfer oil circulation pump P06 and the second inlet of the reboiler E04 of the recovery tower. Control valves are connected by pipelines between the first and second outlets of the hot oil section 4 and the inlet of the heat transfer oil circulation pump P06. The temperature sensor TC is electrically connected to the control valve.

[0033] Example 2

[0034] This embodiment provides a method for monomer recovery during polystyrene production, using the monomer recovery system described in Embodiment 1, and the steps include:

[0035] The devolatilized gas phase from devolatilizer 1 is fed into devolatilizer precooler E01 for primary condensation. The gas phase after primary condensation enters devolatilizer postcooler E02 for secondary condensation. The gas phase after secondary condensation is sent into vacuum system 2. The liquid phase after secondary condensation is returned to polymerization reactor 3 after passing through devolatilizer postcooler D02 and post condensate pump P02.

[0036] After primary condensation, the liquid phase enters the recovery tower C01 for distillation via the pre-cooling tank D01 and the pre-condensate pump P01. Part of the liquid phase after primary condensation enters the reboiler E04 of the recovery tower via the outlet of the recovery tower C01 and the bottom pump P04 for reboiling. Part of the liquid phase is discharged to the waste monomer treatment section 6 via the waste monomer recovery branch after passing through the bottom pump P04. The gas phase generated by reboiling is sent to the recovery tower C01. The recovery tower C01 operates under negative pressure. The gas phase is drawn into the condenser E05 of the recovery tower by the vacuum fan of the recovery tower C01 for condensation. The gas phase generated by condensation is sent to the vacuum system 2, and the liquid phase enters the recovery tower reflux tank D05. The recovery tower reflux tank D05 is equipped with baffles for water-oil separation. The liquid phase containing oil in the recovery tower reflux tank D05 enters the water-cutting tank D06 of the recovery tower and is discharged to the discharge section 5. Another part of the liquid phase is returned to the recovery tower C01 via the reflux pump P05, of which part is returned to the polymerization reactor 3.

[0037] The heat source for the high-temperature heat transfer oil generated by the deheating of the polymerization reactor 3 is the reboiler E04 of the recovery tower. The heat transfer oil is sent from the hot oil section 4 and sent to the reboiler E04 of the recovery tower by the heat transfer oil circulation pump P06 to heat it. After the heat transfer oil heats the reboiler E04 of the recovery tower, the temperature decreases. The temperature can be controlled by replenishing the high-temperature heat transfer oil generated by the deheating of the polymerization reaction.

[0038] Application Examples

[0039] Taking a 120,000-ton / year polystyrene plant as an example, after the 6021 kg / h of devolatilized gas phase passes through the precooler E01, approximately 1844 kg / h of the gas phase (18.4 wt% ethylbenzene, 69.3 wt% styrene, and 4.6 wt% oligomers) is condensed and enters the subsequent recovery tower CO1. The remaining 4177 kg / h of the gas phase (25.4 wt% ethylbenzene and 66.9 wt% styrene) enters the postcooler E02 for further condensation. For the oligomers, after passing through the precooler E01, approximately 99.64% of the oligomers are condensed and enter the downstream recovery tower CO1. The separation parameters are shown in Table 1.

[0040] Table 1

[0041] Oligomer flow rate from the precooler 0.31kg / h Condensed oligomer flow rate 85.02 kg / h Oligomer separation efficiency of the devolatilization precooler 99.64％

[0042] The gas phase output from the pre-cooler E01 is condensed a second time by the post-cooler E02 to obtain 4162 kg / h of condensate, which is returned to the system. The composition of the recovered monomer stream is shown in Table 2.

[0043] Table 2

[0044] Ethylbenzene 25.49 styrene 67.05 oligomers 7.34E-05 other 7.45

[0045] The CO1 distillation in the recovery column yielded 1731 kg / h of recovered monomer, which was returned to the system, while the bottom column yielded 154 kg / h of waste monomer. The specific composition of the top and bottom streams is shown in Table 3.

[0046] Table 3

[0047]

[0048] For oligomers, the separation efficiency of recovery tower CO1 is as high as 99.42 wt%.

[0049] In summary, the vapor phase removed by the devolatilizer in this invention is condensed in two stages; most of the oligomers are condensed into liquid phase in the pre-devolatilization cooler and sent to the recovery tower for refining; the condensate from the post-devolatilization cooler is directly recycled back, reducing the load on the recovery tower system and saving equipment investment and energy consumption; the reboiler heating of the recovery tower uses the warm oil generated by the deheating of the polymerization reactor as the heat source, eliminating the need for additional heating and saving on utility costs.

[0050] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made based on the description and illustrations of the present invention should be included within the protection scope of the present invention.

Claims

1. A monomer recovery system for polystyrene production, characterized in that, include: Deviation precooler (E01), devolatilization postcooler (E02), recovery tower reboiler (E04), recovery tower condenser (E05), devolatilization precooler (D01), devolatilization postcooler (D02), recovery tower reflux tank (D05), recovery tower water cut-off tank (D06), pre-condensate pump (P01), post-condensate pump (P02), tower bottom pump (P04), reflux pump (P05), heat transfer oil circulation pump (P06), and recovery tower (C01); The outlet of the devolatilizer (1) is connected to the inlet of the devolatilization precooler (E01), the outlet of the devolatilization precooler (E01) is connected to the inlet of the devolatilization postcooler (E02), and the liquid outlet of the devolatilization precooler (E01) is connected to the first liquid inlet of the recovery tower (C01); the outlet of the devolatilization postcooler (E02) is connected to the inlet of the vacuum system (2), and the liquid outlet of the devolatilization postcooler (E02) is connected to the liquid inlet of the polymerization reactor (3); the liquid outlet of the recovery tower (C01) is connected to the first liquid inlet of the recovery tower reboiler (E04). The outlet of the reboiler (E04) of the recovery tower is connected to the inlet of the recovery tower (C01); the outlet of the recovery tower (C01) is connected to the inlet of the condenser (E05) of the recovery tower, the outlet of the condenser (E05) of the recovery tower is connected to the vacuum system (2), the outlet of the condenser (E05) of the recovery tower is connected to the inlet of the reflux tank (D05) of the recovery tower; the first outlet of the reflux tank (D05) of the recovery tower is connected to the second inlet of the recovery tower (C01), and the second outlet of the reflux tank (D05) of the recovery tower is connected to the drainage section (5). The outlet of the devolatilization aftercooler (E02) and the inlet of the polymerization reactor (3) are connected in sequence by the devolatilization aftercooler (D02) and the post-condensate pump (P02); one end of the first pressure balancing pipe is connected to the outlet pipe of the devolatilization aftercooler (D02), and the other end of the first pressure balancing pipe is connected to the inlet pipe of the vacuum system (2); The outlet of the precooler (E01) and the first inlet of the recovery tower (C01) are connected in sequence by the precooler tank (D01) and the precondensate pump (P01); one end of the second pressure balancing pipe is connected to the outlet pipe of the precooler tank (D01), and the other end of the second pressure balancing pipe is connected to the inlet pipe of the postcooler (E02). All connections are pipe connections.

2. The monomer recycling system according to claim 1, characterized in that, The reboiler (E04) of the recovery tower is heated by a heat transfer oil circulation pipeline. The first and second outlets of the hot oil section (4) are respectively connected to the inlet pipeline of the heat transfer oil circulation pump (P06). The outlet of the heat transfer oil circulation pump (P06) is connected to the second inlet pipeline of the reboiler (E04) of the recovery tower. The outlet of the reboiler (E04) of the recovery tower is connected to the inlet pipeline of the hot oil section (4) and the inlet pipeline of the heat transfer oil circulation pump (P06). A temperature sensor (TC) is also connected between the outlet of the heat transfer oil circulation pump (P06) and the second inlet of the reboiler (E04) of the recovery tower. A control valve is connected between the first and second outlets of the hot oil section (4) and the inlet of the heat transfer oil circulation pump (P06). The temperature sensor (TC) is electrically connected to the control valve.

3. The monomer recycling system according to claim 1, characterized in that, The outlet of the recovery tower (C01) is connected to the first inlet of the recovery tower reboiler (E04) by a pipeline of the bottom pump (P04); a waste monomer recovery branch is provided between the bottom pump (P04) and the first inlet of the recovery tower reboiler (E04), and the outlet of the waste monomer recovery branch is connected to the pipeline of the waste monomer treatment section (6).

4. The monomer recycling system according to claim 1, characterized in that, The reflux pump (P05) is connected by a pipeline between the first outlet of the recovery tower reflux tank (D05) and the second inlet of the recovery tower (C01).

5. The monomer recycling system according to claim 4, characterized in that, A monomer recovery branch is provided between the reflux pump (P05) and the second inlet of the recovery tower (C01), and the outlet of the monomer recovery branch is connected to the inlet of the polymerization reactor (3).

6. The monomer recycling system according to claim 1, characterized in that, One end of the third pressure balancing pipe is connected to the outlet pipe of the recovery tower reflux tank (D05), and the other end of the third pressure balancing pipe is connected to the inlet pipe of the recovery tower condenser (E05).

7. The monomer recycling system according to claim 1, characterized in that, The second outlet of the recovery tower reflux tank (D05) is connected to the drainage section (5) by a pipeline of the recovery tower water cutter tank (D06), and the outlet of the recovery tower water cutter tank (D06) is connected to the inlet pipeline of the vacuum system (2).

8. A method for monomer recovery in a polystyrene production process, employing the monomer recovery system as described in any one of claims 1-7, characterized in that the steps... include: The devolatilized gas phase from the devolatilizer (1) is fed into the devolatilization precooler (E01) for primary condensation. The gas phase after primary condensation is fed into the devolatilization postcooler (E02) for secondary condensation. The liquid phase after primary condensation is fed into the recovery tower (C01) for distillation. The gas phase after secondary condensation is sent into the vacuum system (2), and the liquid phase after secondary condensation is returned to the polymerization reactor (3). The gas phase after distillation is sent into the vacuum system (2), the first liquid phase after distillation is returned to the recovery tower (C01), the second liquid phase is returned to the polymerization reactor (3), and the third liquid phase is fed into the discharge section (5).

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